A rotary joint is used for connecting a flow passage in a fixed-side member to a flow passage in a rotary-side member. For example, a chemical mechanical polishing apparatus (CMP apparatus) is used for performing surface polishing treatment of a semiconductor wafer. In the CMP apparatus, fluids such as a polishing solution, air for pressurization, washing water, pure water, air for air blow, a polishing residue liquid, and the like flow between a rotary-side member (a turntable or a top ring) and a fixed-side member (a CMP apparatus main body) which supports the rotary-side member. In order to allow such fluids to flow between the rotary-side member and the fixed-side member without mixing of these fluids, a joint portion that connects these members requires a plurality of independent fluid passages. Thus, for example, a multi-port rotary joint disclosed in Patent Literature 1 is used as such a joint portion.
FIG. 13 is a cross-sectional view of a conventional rotary joint. The rotary joint includes: a tubular case body 80; a shaft body 83 provided rotatably within the case body 80; and a plurality of mechanical seals 86 provided in a space 84 between the case body 80 and the shaft body 83. Each mechanical seal 86 includes first sealing rings 91 which are attached to the case body 80; second sealing rings 92 which rotate with the shaft body 83; and a plurality of coil springs 97. A plurality of independent fluid passages 85 are provided in the rotary joint.
The shaft body 83 includes a shaft main body 87 and sleeves 89 fitted externally on the shaft main body 87. The sleeves 89 are arranged along an axial direction alternately with the second sealing rings 92 of the mechanical seals 86. A pressing member 90 is fastened to the shaft main body 87 by a bolt 90a, whereby the sleeves 89 and the second sealing rings 92 are pressed in the axial direction. By the pressing force of the pressing member 90, the second sealing rings 92 and the sleeves 89 are pressed against each other, so that all the sleeves 89 and second sealing rings 92 are rotatable with the shaft main body 87 due to frictional forces therebetween.
In the case body 80, first flow passages 81 are formed so as to be opened at the outer peripheral side and the inner peripheral side thereof. In the shaft body 83 which includes the shaft main body 87 and the sleeves 89, second flow passages 82 are formed so as to be opened at the outer peripheral side thereof. In the shaft main body 87, flow passage holes 87a are formed as portions of the second flow passages 82, and in an axially central portion of each sleeve 89, a through hole 88 is formed as the other portion of the second flow passage 82. Each through hole 88 is connected to the flow passage hole 87a and serves as an opening hole of the second flow passage 82 at the outer peripheral side.
O-rings 93 are provided between the shaft main body 87, the sleeves 89, and the second sealing rings 92, thereby preventing a fluid flowing through each second flow passage 82 from entering another flow passage or leaking to the outside.
One first flow passage 81 and one second flow passage 82 are opened at the same height position in the axial direction and form one independent fluid passage 85. Thus, the mechanical seals 86 are provided in the space 84. That is, the first sealing rings 91, 91 of the mechanical seal 86 are provided at the radially outer side of each sleeve 89 and between the second sealing rings 92, 92 adjacent to each other across the sleeve 89, and an annular flow passage 96 is formed between these first sealing rings 91, 91 so as to connect the second flow passage 82 (the through hole 88) to the first flow passage 81.
The coil springs 97 of each mechanical seal 86 press the first sealing rings 91 against the second sealing rings 92 in the axial direction, so that the first sealing rings 91 contact with the second sealing rings 92 located adjacently thereto in the axial direction, thereby preventing a fluid from leaking through between the contacting surfaces thereof. That is, a portion of a side surface, in the axial direction, of each first sealing ring 91 is a first seal surface 91a, and a portion of an annular side surface of each second sealing ring 92 is a second seal surface 92a which slidably contacts with the first seal surface 91a. A fluid to be sealed partially enters between the first seal surface 91a and the second seal surface 92a to form a lubricating film between the seal surfaces 91a, 92a, thereby obtaining a lubricating effect.
Due to the above configuration, the shaft main body 87, the sleeves 89, and the second sealing rings 92 are rotatable together relative to the case body 80, and the rotating second sealing rings 92 slidably contact with the first sealing rings 91 which are at a stationary side, so that the function as the mechanical seals 86 is exerted, whereby the independent fluid passages 85 are formed.